Ignition-quenching covers and methods for aerospace applications

ABSTRACT

Ignition-quenching covers are configured to quench an ignition event in a combustible environment triggered by an ignition source associated with an ignition-risk structure. Ignition-quenching covers comprise a porous body that includes two or more porous elements and are configured to cover the ignition-risk structure, wherein the ignition-risk structure is associated with a potential ignition source that may produce the ignition event in the combustible environment. The porous body defines passages sized to quench the ignition event. Methods comprise installing a porous ignition-quenching cover over an ignition-risk structure to prevent bulk combustion, e.g., of a fuel vapor in a fuel tank, due to an ignition event associated with the ignition-risk structure.

RELATED APPLICATION

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 14/805,259, filed on Jul. 21, 2015 and entitledIGNITION-QUENCHING SYSTEMS, APPARATUSES, AND METHODS, which issued Dec.24, 2019 as U.S. Pat. No. 10,512,805, the complete disclosure of whichis incorporated herein by reference.

FIELD

The present disclosure relates to systems, apparatuses, and methods forquenching ignition in aerospace applications, such as in connection withaircraft fuel tanks.

BACKGROUND

In many situations, devices must operate in potentially hazardousconditions, such as where a fuel mixture may be ignited by uncontrolledoperating or environmental conditions. For example, vehicles, includingaerospace vehicles, typically operate with a fuel that must bemaintained in a safe condition during storage and use. The ignitionhazard should be minimized even when the vehicle is subject touncontrolled events such as an accident, electrical malfunction, alightning strike, or static electrical discharge. Other applicationsrequiring ignition hazard consideration include fuel transport, fuelstorage, mining operations, chemical processing, metal fabrication,power plant construction and operation, and operations which involvecombustible particulate such as sawdust, metal, flour, and grain.

In the aerospace industry, lightning strikes of aircraft are a concernbecause they could result in electrical arcs and/or heating sufficientto ignite vaporous fuel mixtures. Though lightning passes throughaircraft virtually always without resulting harm, newer aircraft designsincorporating composite materials include less metal to shunt and/ordissipate the energy of a lightning strike.

Design of apparatuses exposed to ignition hazards typically involvesreducing the likelihood of ignition, containing the ignition hazard,and/or withstanding the ignition hazard. Electrically conductivestructures, such as fasteners, may join and/or support compositestructural components within potentially combustible environments, suchas within a fuel tank. These electrically conductive structures maybecome a focal point for electromagnetic effects (e.g., arcing,electrostatic discharge, heating, and/or hot particle ejection), e.g.,due to lightning strikes.

Conventionally, metal fasteners in a composite fuel tank are isolatedfrom the fuel volume by sealant and/or a seal cap. The sealant and/orseal cap are configured to physically and/or electrically separate themetal fastener from the fuel volume and to contain the ignition hazard.However, electromagnetic effects may generate heat and pressuretransients that may damage the seal. Additionally, seals may be subjectto temperature cycles due to, e.g., daily solar heating and/or operationin the atmosphere. The temperature cycling may lead to increasedsusceptibility to damage from electromagnetic effects and/or ignitionevents.

SUMMARY

Ignition-quenching covers are configured to quench an ignition event ina combustible environment triggered by an ignition source associatedwith an ignition-risk structure. The ignition-risk structure isassociated with a potential ignition source that may produce theignition event in the combustible environment. In some examples, theignition-quenching cover comprises a porous body that includes two ormore porous elements, the ignition-quenching cover is configured tocover the ignition-risk structure, and the porous body defines passagessized to quench the ignition event.

Methods of preventing bulk combustion of a fuel vapor by an ignitionevent associated with an electrically conductive fastener in a compositestructure fuel tank also are disclosed. Some methods comprise installinga porous ignition-quenching cover over the electrically conductivefastener in the composite structure fuel tank to at least partiallyenclose the electrically conductive fastener. The porousignition-quenching cover is configured to quench the ignition eventtriggered by an ignition source associated with the electricallyconductive fastener.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary side elevation representation of anignition-quenching system.

FIG. 2 is a fragmentary view of an example of a porous body.

FIG. 3 is a fragmentary view of an example of a multicomponent porousbody.

FIG. 4 is a schematic representation of ignition-quenching systemmanufacturing methods according to the present disclosure.

FIG. 5 is a schematic representation of ignition-quenching covermanufacturing methods according to the present disclosure.

DESCRIPTION

FIGS. 1-5 provide examples of systems, apparatuses, and methods forquenching ignition. In general, in the drawings, elements that arelikely to be included in a given embodiment are illustrated in solidlines, while elements that are optional or alternatives are illustratedin dashed lines. However, elements that are illustrated in solid linesare not essential to all embodiments of the present disclosure, and anelement shown in solid lines may be omitted from a particular embodimentwithout departing from the scope of the present disclosure. Elementsthat serve a similar, or at least substantially similar, purpose arelabeled with numbers consistent among the figures. Like numbers in eachof the figures, and the corresponding elements, may not be discussed indetail herein with reference to each of the figures. Similarly, allelements may not be labeled or shown in each of the figures, butreference numerals associated therewith may be used for consistency.Elements, components, and/or features that are discussed with referenceto one or more of the figures may be included in and/or used with any ofthe figures without departing from the scope of the present disclosure.

FIG. 1 is a schematic representation of an ignition-quenching system 100that includes an ignition-quenching cover 110. The ignition-quenchingcover 110 (also called an ignition arrestor) covers an ignition-riskstructure 140 that extends and/or protrudes from a support structure150. The ignition-risk structure 140 is a structure associated with apotential ignition source, e.g., a fastener potentially subject toelectromagnetic effects that may produce arcing at the fastener.

Ignition-quenching systems 100 may include a combustible environment160. Additionally or alternatively, ignition-quenching system 100,and/or components thereof, may be configured for contact and/orutilization with the combustible environment 160 (e.g., chemicallyresistant to and/or chemically nonreactive with combustible environment160). Combustible environment 160 is combustible and includes acombustible substance and/or mixture. For example, combustibleenvironment 160 may include a fuel (e.g., hydrogen, gaseous, liquid,and/or aerosolized hydrocarbon, and/or suspended particulate such assawdust, etc.), an oxidizer (e.g., oxygen, fluorine, and/or nitrousoxide), and optional non-reactive diluent (e.g., nitrogen, argon, and/orhelium) with concentrations within the flammability limits of thefuel/oxidizer mixture. As another example, combustible environment 160may include a gas that undergoes explosive decomposition (e.g.,acetylene, nitrous oxide). Additional specific examples of fuels includemotor fuels such as automotive fuel, diesel fuel, aviation fuel, and/orjet fuel. Combustible environment 160 may include gases, vapors,aerosols, and/or particulate.

Ignition-quenching cover 110 has a proximal cover side 112 and a distalcover side 114. The proximal cover side 112 is configured to face theignition-risk structure 140 and the support structure 150. The proximalcover side 112 may be referred to as the interior surface of theignition-quenching cover 110. The distal cover side 114 is opposite theproximal cover side 112. The distal cover side 114 is configured to facetowards a bulk 162 of the combustible environment 160 and to facegenerally away from the ignition-risk structure 140 and the supportstructure 150. Distal cover side 114 may be referred to as the exteriorsurface of the ignition-quenching cover 110.

Ignition-quenching cover 110 is porous, permitting the combustibleenvironment 160 to permeate into and through the ignition-quenchingcover 110 and to contact the ignition-risk structure 140.Ignition-quenching cover 110 includes, and may be essentially composedof, a porous body 120 that is configured to permit the combustibleenvironment 160 to permeate into and through the porous body 120. Thebulk 162 of the combustible environment 160 is the portion of thecombustible environment 160 not within the ignition-quenching cover 110and not enclosed by the ignition-quenching cover 110 between theproximal cover side 112 and the ignition-risk structure 140 and/or thesupport structure 150. The volume between the proximal cover side 112and the ignition-risk structure 140 and/or the support structure 150 isan enclosed volume 164 of the ignition-quenching cover 110. The volumewithin the ignition-quenching cover 110 (e.g., the volume between theproximal cover side 112 and the distal cover side 114) that isaccessible to the combustible environment 160 is an interior volume 166of the ignition-quenching cover 110 (also referred to as the porevolume). The enclosed volume 164 and the interior volume 166 aresubstantially less than the volume of the bulk 162 of the combustibleenvironment 160.

Ignition-quenching cover 110 is configured to prevent an ignition sourceoriginating from the ignition-risk structure 140 (e.g., due toelectromagnetic effects) from igniting the bulk 162 of the combustibleenvironment 160. That is, an ignition source confined by theignition-quenching cover 110 is prevented from producing substantialand/or undesirable combustion (e.g., explosive combustion) in the bulk162 of the combustible environment 160. Examples of ignition sourcesinclude an electrical arc, a hot surface, a hot particle ejection,and/or an electrostatic discharge (e.g., due to internal friction and/ortribocharging).

Without the ignition-quenching cover 110, an ignition source within thecombustible environment 160 would generate an ignition kernel (a smallvolume of combustion initiated by the energy imparted by the ignitionsource). Typically, but not necessarily, an ignition source would createa region of energetic gas that has high pressure and high temperatureover a time scale during which the gas is essentially not moving (i.e.,the energy deposition from the ignition source would be essentiallyimpulsive). Due to this energy deposition, the energetic gas will expandinto the surrounding gas that had been unaffected by the energydeposition. The sudden expansion of the energetic gas creates a pressurewave which may be acoustic or supersonic. If the pressure wave issufficiently energetic, it may cause direct ignition of the combustionreactants (e.g., detonation).

The ignition-quenching cover 110 generally is configured to quenchignition from an ignition source that does not pose a direct ignitionrisk due to the associated pressure wave. For example, typical ignitionsources to be mitigated by the ignition-quenching cover 110 impart lessthan 1 J (joules) or less than 0.1 J (and typically more than 1 μl(microjoules) or more than 10 u_1). Such lower energy ignition sourcesmay generate weak shock waves and/or pressure waves with a pressureamplitude less than about 100 kPa (kilopascals). Further,ignition-quenching cover 110 may be configured to withstand a pressurewave (if any) generated by an ignition source enclosed by theignition-quenching cover 110, for example, by being porous enough topermit gas pressure equalization across the ignition-quenching cover110. The ignition-quenching cover 110 may be configured to impede and/ordissipate the pressure wave and may be configured to permit the pressurewave to pass substantially unimpeded.

Without the ignition-quenching cover 110, the ignition kernel wouldgenerate hot gases and/or hot particles that are a direct ignition risk.These reaction products may drive a self-propagating combustion reaction(an established flame front, e.g., a deflagration wave or detonationwave) that would consume all of the available combustion reactants.Flame arrestors may be placed in the path of the established flame frontto limit the propagation of the flame front. For example, flamearrestors may be placed in fuel fill tubes to prevent an establishedflame front from propagating through the fuel fill tube. Flame arrestorstypically are installed in a transfer path, such as a fill tube, a pourspout, and/or conduit, and therefore are configured to permit flow ofgas and liquid substantially unimpeded. Ignition-quenching cover 110 isconfigured to prevent the formation of an ignition kernel due to anignition source and/or to prevent propagation of a nascent flame frontoriginating from the ignition kernel. That is, the ignition-quenchingcover 110 may be configured to prevent ignition of the combustibleenvironment 160 within the enclosed volume 164 and may be configured toquench and/or extinguish ignition within and/or in proximity to theignition-quenching cover 110 (e.g., within the enclosed volume 164and/or the interior volume 166). Thus, if an ignition source does ignitean ignition kernel within the enclosed volume 164, the nascent flamefront generated by the ignition kernel does not pass through and/oraround the ignition-quenching cover 110. The nascent flame front isquenched before the nascent flame front could contact the bulk 162 ofthe combustible environment 160 and establish a self-propagating flamefront. Together, the ignition kernel, the associated nascent flamefront, and the associated pressure wave within the enclosed volume 164may be referred to as an ignition event. The ignition-quenching cover110 is configured to prevent, mitigate, and/or suppress one or moreaspects of an ignition event triggered (ignited) by an ignition sourceassociated with the ignition-risk structure 140.

Because the ignition-quenching cover 110 is configured to quench,extinguish, and/or suppress combustion (an ignition event) within and/orin proximity to the ignition-quenching cover 110, the ignition-quenchingcover 110 does not need to quench an established flame front like adeflagration wave. By preventing further combustion when the combustedregion is small, the requirements to withstand heat and/or pressure arelikewise small, as compared to the requirements to stop an establishedflame front. Similarly, the potential combusted volume of thecombustible environment 160 is smaller if combustion is stopped at thesource rather than at a distant location in the path of the establishedflame front.

Ignition-quenching cover 110 may be configured to prevent formation,propagation, and/or maturation of an ignition kernel therein bydissipating heat energy associated with the ignition source and/or theignition kernel. An ignition kernel may mature into a self-propagatingcombustion reaction (e.g., a deflagration wave) when heat energy fromthe reaction sufficiently heats neighboring combustion reactants (i.e.,when energy released is greater than energy losses). Ignition-quenchingcover 110 may be configured to dissipate heat energy that may otherwiseserve to sustain a combustion reaction. For example, the porous body 120may have a surface area to pore volume ratio that is high enough toprevent combustion from propagating through the porous body 120 becauseof the thermal contact between the porous body 120 and the combustibleenvironment 160 within the porous body 120.

Porous body 120 and/or ignition-quenching cover 110 may have a specificheat capacity that is greater, typically much greater, than the specificheat capacity of combustible environment 160. For example, the porousbody 120, and/or components thereof, may have a volumetric specific heatcapacity that is at least 10 times, at least 100 times, or at least1,000 times the volumetric specific heat capacity of the combustibleenvironment 160. Porous body 120 and/or ignition-quenching cover 110 mayhave a total heat capacity that is greater, typically much greater, thanthe total heat capacity of combustible environment 160 within the volumedefined by the exterior dimensions of the corresponding porous body 120and/or ignition-quenching cover 110. For example, the porous body 120,and/or components thereof, may have a total heat capacity that is atleast 3 times, at least 10 times, or at least 30 times the total heatcapacity of the combustible environment 160 within the volume defined bythe exterior dimensions of the porous body 120. Porous body 120 ofignition-quenching cover 110 may have a thermal conductivity that isgreater, typically much greater, than the thermal conductivity ofcombustible environment 160. For example, the porous body 120, and/orcomponents thereof, may have a thermal conductivity that is at least 5times, at least 10 times, at least 100 times, or at least 1,000 timesthe thermal conductivity of the combustible environment 160. As aspecific comparison, air and combustible gases have a volumetricspecific heat capacity of about 1 kJ/(m³·K) (kilojoules per meter-cubedkelvin) and a thermal conductivity of about 0.03 W/(m·K) (watts permeter kelvin), while the comparable values for examples ofignition-quenching cover 110 materials are 2,400 kJ/(m³·K) and 170W/(m·K) (for aluminum), and 2,000 kJ/(m³·K) and 0.25 W/(m·K) (forpolyamide 6/6, also sold as NYLON 6/6 polymer).

Ignition-quenching cover 110 may be configured to prevent the ignitionof combustible environment 160 by preventing a hot particle that isemitted from ignition-risk structure 140 from traveling through theignition-quenching cover 110 and/or the porous body 120. As used herein,the term “hot particle” refers to a particle that is emitted fromignition-risk structure 140 and/or due to an ignition source at theignition-risk structure 140 that has a size and/or a thermal energysufficient to cause ignition of combustible environment 160. Porous body120 and/or ignition-quenching cover 110 may be configured such that noparticle larger than a predetermined size may fully pass through porousbody 120 along a straight-line trajectory without colliding with astructural element of porous body 120 and thereby losing at least aportion of its thermal and/or kinetic energy. For example, and asdiscussed further herein, porous body 120 may be constructed of one ormore foams and/or lattices that lack a straight-line open pathconnecting proximal cover side 112 and distal cover side 114 that wouldallow unimpeded transit of a particle greater than a predetermined size.

A combustible substance in a given set of environmental conditions maybe characterized by a quenching distance that is defined as the smallestdiameter of a tube through which a flame front in the combustiblesubstance may propagate. Porous body 120 includes pores 122 and/orpassages 126 (as best seen in the examples of FIG. 2 ) that are sizedand/or arranged to prevent a nascent flame front from passing throughignition-quenching cover 110. For instance, a characteristic pore sizeand/or a characteristic passage size of porous body 120, as discussed inmore detail herein, may be smaller than a quenching distance, or relatedparameter, of combustible environment 160, such that an ignition kerneland/or a nascent flame front that originates at ignition-risk structure140 (e.g., within enclosed volume 164) is quenched within the interiorvolume 166 before the ignition kernel and/or the flame front may reachdistal cover side 114.

Porous body 120 includes, and may be composed essentially of, one ormore porous elements 130. As detailed in the example internal views ofFIG. 2 , porous body 120 and porous elements 130 each include aplurality of pores 122 (also called cells) and a plurality of struts 124(also called trusses and/or ligaments) that together form a mesh, anetwork, a lattice, a matrix, and/or a foam structure. Struts 124 arestructural components that adjoin and/or define pores 122. Examples ofstruts include beam-like structural elements of a lattice structure,cell faces of a foam, and cell edges of a foam. The structure of theporous body 120 and/or the porous elements 130 may be ordered,disordered, or may include regions of order and/or disorder. Hence, thepores 122 and/or the struts 124 of the porous body 120 may be describedas ordered, disordered, regular, irregular, patterned, repetitive,random, and/or chaotic. The left internal view of FIG. 2 shows anexample of a relatively disordered pore 122 and strut 124 network, witha distribution of pores 122 and struts 124 in an irregular pattern. Theright internal view of FIG. 2 shows an example of a relatively orderedpore 122 and strut 124 network, with relatively uniformly sized andspaced pores 122 and struts 124.

The pores 122 (of porous body 120 and porous elements 130) generally areinterconnected and form passages 126 (also called channels) that permitgas and/or liquid flow through the porous body 120. Hence, porous body120 and porous elements 130 may be described as gas permeable and/orliquid permeable. The porous body 120 may be configured to havesignificant flow resistance to gas flow and/or liquid flow (such as flowof liquid fuel) provided that the flow resistance is sufficiently lowenough to withstand a pressure wave associated with an ignition source.Alternatively, the porous body 120 may be configured to have arelatively low resistance to gas flow through the porous body 120; gasmay flow substantially freely through the porous body 120 and a pressurewave would be substantially unimpeded. Porous body 120 and/or porouselements 130 may include, and/or may be, a reticulated lattice, areticulated foam, and an open-cell foam.

Porous body 120 and/or porous elements 130 may be characterized by thesizes of the respective pores 122 (such as the volumes, areas, and/oreffective diameters of pores 122), the sizes of the respective struts124 (such as volumes, cross sectional areas, and/or lengths of struts124), and/or characteristics of the passages 126 (such as averageeffective diameter, spacing, density, and/or average orientation of thepassages 126). Pores 122 and/or struts 124 within a porous structure(porous body 120 or porous elements 130) may be approximately equal insize (e.g., all pores 122 substantially the same size) and may have adistribution of sizes. For example, porous body 120 and/or porouselements 130 may be characterized by a minimum pore size, a maximum poresize, an average (i.e., a mean) pore size, a standard deviation of poresizes, a distribution of pore sizes, and/or any other suitable metric.As another example, porous body 120 and/or porous elements 130 may becharacterized by a minimum, maximum, and/or average characteristic sizeof the passages 126 (e.g., the effective diameter of each passage 126).Generally, the effective diameters of the pores 122 and/or passages 126of the porous body 120 are less than the quenching distance of thecombustible environment 160 and sized to permit a pressure waveassociated with an ignition event to flow through the porous body 120and/or to dissipate within the porous body 120. As discussed herein, themaximum effective diameter of pores 122 and/or the maximum effectivediameter of passages 126 of individual porous elements 130 may be largerthan the quenching distance of the combustible environment 160. Withinthe porous body 120 and/or the porous elements 130, the averageeffective diameter of pores 122 and/or the average effective diameter ofpassages 126 may be at least 0.1 mm (millimeters), at least 0.2 mm, atleast 0.5 mm, at least 1 mm, at least 2 mm, at least 3 mm, at most 10mm, at most 3 mm, at most 1 mm, at most 0.3 mm, and/or at most 0.1 mm.Struts 124 may have an average diameter that is at most 75%, at most50%, at most 25%, at most 10%, and/or at most 5% of the averageeffective diameter of the respective pores 122 and/or passages 126.

Ignition-quenching cover 110 and/or porous body 120 may have a massdensity that is less, typically much less, than the mass density of thematerials that form the respective ignition-quenching cover 110 orporous body 120. The mass density of ignition-quenching cover 110 and/orporous body 120 is the mass of the respective structure divided by theexterior volume of the respective structure (the volume defined by theexterior dimensions of the structure). The exterior volume of therespective structure includes the open pore volume and any enclosedvoids of the structure. For example, the exterior volume of theignition-quenching cover 110 is the volume defined by the proximal coverside 112 and the distal cover side 114 and includes the interior volume166, but not the volume of an optional cavity 116 (as discussed furtherherein). Ignition-quenching cover 110 and/or porous body 120 may have amass density that is at most 2 g/cc (grams per cubic centimeter), atmost 1 g/cc, at most 0.5 g/cc, at most 0.2 g/cc, at most 0.1 g/cc, atmost 0.05 g/cc, at most 0.02 g/cc, or at most 0.01 g/cc.

Ignition-quenching cover 110 and/or porous body 120 may be characterizedby a porosity. The porosity of ignition-quenching cover 110 and/orporous body 120 is the total open volume of the pores 122 (e.g., theinterior volume 166) divided by the exterior volume of the respectivestructure. The porosity of the respective structure may be described asthe volume fraction of the pores 122 and/or the volume fraction notoccupied by the struts 124 or other structural elements. The porosity ofthe ignition-quenching cover 110 and/or the porous body 120 may be atleast 50%, at least 75%, at least 85%, at least 90%, at least 95%, andat least 98%.

Struts 124 of porous body 120 and/or porous elements 130 may include oneor more hollow struts 128. Hollow struts 128 may be hollow and mayinclude open or closed voids (for instance, one or more hollow struts128 may be hollow tubes). The internal voids of one or more struts 124may be interconnected. The majority of, or all, struts 124 may be hollowstruts 128. Hollow struts 128 may be sized to reduce the weight ofporous body 120 and/or porous elements 130, while maintaining thestructural integrity of the respective structure, relative to a similarporous structure incorporating solid struts. Hollow struts 128 may beconfigured to rupture responsive to a force greater than a predeterminedthreshold magnitude, such as a force that may be associated with apressure wave associated with an ignition event. The hollow struts 128may contain an inert gas or a flame-suppressing substance such as ahaloalkane. In such an embodiment, the rupturing of hollow strut 128 asa result of an ignition event associated with the ignition-riskstructure 140 may release the flame-suppressing substance, which mayserve to mitigate the propagation of the ignition kernel andcorresponding nascent flame front and/or quench the ignition evententirely.

As shown in the example of FIG. 3 , porous body 120 may be amulticomponent structure (e.g., a multilayer structure) that includestwo, three, four, or more porous elements 130. Each porous element 130independently may have a passage orientation 132, an average passagesize, an average pore size, an average passage spacing, and/or a passagedensity. For example, one porous element 130 may have one or morecharacteristics that are different than the correspondingcharacteristics of another porous element 130 within the same porousbody 120. Additionally or alternatively, porous body 120 may include oneor more porous elements 130 and a flexible exterior layer that isconfigured to elastically deform in response to a pressure waveassociated with an ignition event. The flexible exterior layer may ormay not be porous.

Passage orientation 132 may be defined by an average direction ofpassages 126 through the porous element 130 and/or by an averagedirection between opposite faces of the porous element 130 (e.g.,proximal and distal faces of the porous element corresponding to theproximal cover side 112 and the distal cover side 114 of theignition-quenching cover 110). In the example of FIG. 3 , each porouselement 130 has a different passage orientation 132, each defined by anordered array of pores 122 and struts 124 (e.g., each porous element 130is a regular lattice of struts 124).

By selecting and/or arranging the passage orientation 132, the averagepassage size, the average pore size, the average passage spacing, and/orthe passage density of each porous element 130 and/or by selectingand/or arranging the relative alignment of the porous elements 130, theporous body 120 may be configured to have a maximum (and/or an average)passage size, pore size, and/or passage spacing less than apredetermined threshold, such as the quenching distance, or a relatedparameter, of the combustible environment 160. Similarly, porous body120 may be configured to have a minimum and/or average passage densitygreater than a predetermined threshold, such as a parameter related tothe quenching distance of the combustible environment 160. Though porousbody 120 is configured to quench ignition within the combustibleenvironment 160, individual porous elements 130 may have characteristicsinsufficient to quench ignition within the combustible environment 160.

The passage orientation 132, the average passage size, the average poresize, the average passage spacing, and/or the passage density of eachporous element 130 of the porous body 120 may be selected and/orarranged to prevent the passage of a hot particle larger than apredetermined size. For example, the porous elements 130 of the porousbody 120 may be aligned (by rotation and/or translation) such that thenumber and/or size of straight-line passages 126 through the porous body120 are reduced with respect to the number and/or size of straight-linepassages 126 through any of the porous elements 130. For example, and asshown in the example of FIG. 3 , two otherwise identical porous elements130 that are characterized by a regular lattice may be joined into aporous body 120 with each porous element 130 having a unique passageorientation 132 (and/or lattice orientation). Each porous element 130individually has straight-line passages 126 through the respectiveporous element 130. However, the combination of porous elements 130 atdifferent passage orientations 132 results in no straight-line passages126 through the entire porous body 120.

Returning generally to FIG. 1 , porous body 120 and/or one or moreporous elements 130 may include, and/or may be formed of, anelectrically insulating material, which may serve to electricallyisolate ignition-risk structure 140 from the bulk 162 of combustibleenvironment 160. Additionally or alternatively, porous body 120 and/orone or more porous elements 130 may include, and/or may be formed of, anelectrically conductive material, which may serve as an electromagneticshield to isolate ignition-risk structure 140. When porous body 120includes porous elements 130 that are electrically conductive as well asporous elements 130 that are electrically insulating, the net structuremay be characterized as being electrically conductive or electricallyinsulating, and/or may be characterized by a net electrical impedance.

Ignition-quenching cover 110 and/or porous body 120 may have a net shapethat is configured to prevent a corona discharge on an external surfaceof the respective structure (e.g., the distal cover side 114). Forinstance, the exterior surface of the ignition-quenching cover 110and/or the porous body 120 may be hemispherical. Additionally oralternatively, the exterior surface may be polished or smoothed toensure that the exterior surface does not define sharp points or edgesthat may concentrate an electric field and lead to an electromagneticdischarge.

Porous body 120 and porous elements 130, each independently, mayinclude, and/or may be composed essentially of, a polymer (e.g.,polypropylene, polystyrene, polyurethane, ethylene vinyl acetate (EVA),and/or polysulfone), a composite material (e.g., a carbonfiber-reinforced polymer (CFRP) and/or fiberglass), a ceramic, a glass,a non-metal, and/or a metal (e.g., aluminum, steel, and/or titanium).

Ignition-quenching cover 110 may be sized to cover and/or to encloseignition-risk structure 140 and/or may be installed on or nearignition-risk structure 140. For instance, ignition-quenching cover 110may be configured to substantially enclose at least a portion ofignition-risk structure 140 that is in contact with combustibleenvironment 160. That is, ignition-quenching cover 110 may be configuredsuch that ignition-risk structure 140 is substantially surrounded by oneor both of support structure 150 and/or ignition-quenching cover 110when ignition-quenching cover 110 is installed on ignition-riskstructure 140. Additionally or alternatively, ignition-quenching cover110 may be sized to cover and/or to enclose more than one ignition-riskstructure 140. For example, ignition-quenching cover 110 may be in theform of a porous strip or sheet that may cover a series of ignition-riskstructures 140.

When assembled in the ignition-quenching system 100, theignition-quenching cover 110 and the ignition-risk structure 140 arecollocated, with the ignition-quenching cover 110 covering and/orenclosing the ignition-risk structure 140. The ignition-quenching cover110 is proximate to the ignition-risk structure 140, but not necessarilyin contact with the ignition-risk structure 140. Where the proximalcover side 112 does not contact the ignition-risk structure 140, thedistance between the proximal cover side 112 and the ignition-riskstructure 140 generally is not overwhelmingly larger than the quenchingdistance of the combustible environment 160. For example, the maximumdistance between the proximal cover side 112 and the ignition-riskstructure 140 may be less than 100 times, less than 30 times, less than10 times, less than 3 times, or less than 1 times the quenching distanceof the combustible environment 160. The maximum distance between theproximal cover side 112 and the ignition-risk structure 140 may be atmost 100 mm, at most 30 mm, at most 10 mm, at most 3 mm, or at most 1mm.

Ignition-quenching cover 110 may be coupled to ignition-risk structure140 and/or to support structure 150. For instance, ignition-quenchingcover 110 may be affixed to ignition-risk structure 140 and/or tosupport structure 150 by an adhesive. Additionally or alternatively,ignition-quenching cover 110 may be configured to thread onto, snaponto, and/or mechanically interlock with at least a portion ofignition-risk structure 140. For instance, at least a portion ofignition-quenching cover 110 may be constructed monolithically with atleast a portion of ignition-risk structure 140. As an example,ignition-risk structure 140 may be an assembly of a bolt and a nut thatis configured to thread onto the bolt. The nut may be integrally formedwith ignition-quenching cover 110, such that threading the nut onto thebolt serves to operatively couple ignition-quenching cover 110 toignition-risk structure 140.

Ignition-quenching cover 110 may be configured to receive and/or toengage ignition-risk structure 140, for instance, with a cavity 116defined by proximal cover side 112 of ignition-quenching cover 110.Cavity 116 may be referred to as a recess, a concavity, and/or adepression. Cavity 116, when present, may be configured, sized, and/orshaped to receive and/or to engage a portion of ignition-risk structure140. Cavity 116 may define a cavity volume that may be configured tosurround a substantial portion of ignition-risk structure 140 exposed tothe combustible environment 160 when the ignition-quenching cover 110 isinstalled on ignition-risk structure 140. The enclosed volume 164 of theignition-quenching cover 110 includes the optional cavity volume.

When assembled in the ignition-quenching system 100, theignition-quenching cover 110 and/or the porous body 120 may be in directcontact with ignition-risk structure 140 and/or support structure 150.For example, at least a portion of proximal cover side 112 and/or cavity116 may contact ignition-risk structure 140 and/or support structure150. Additionally or alternatively, at least a portion of porous body120 may be spaced apart from ignition-risk structure 140 and/or supportstructure 150.

Where the proximal cover side 112 is spaced apart from support structure150, the proximal cover side 112 and the support structure 150 maydefine a gap 118 therebetween. The gap 118 may be at least partiallyfilled with a spacer, adhesive, and/or fastener, and may include one ormore unfilled regions. When present, the unfilled regions are sizedand/or arranged to prevent a nascent flame front and/or a hot particlefrom propagating around the ignition-quenching cover 110 and potentiallyigniting the bulk 162 of the combustible environment 160. For example,the unfilled regions of the gap 118 may be smaller than the quenchingdistance, or related parameter, of the combustible environment 160.

Ignition-risk structure 140 may be coupled to, extend from, and/orprotrude from support structure 150 such that at least a portion ofignition-risk structure 140 is in contact with combustible environment160 when combustible environment 160 is present. As shown in FIG. 1 ,ignition-risk structure 140 may extend fully through support structure150 (indicated in dotted line), may terminate within support structure150, or may be supported by and/or coupled to support structure 150without penetrating support structure 150 (indicated in solid line).

Ignition-risk structure 140 may join and/or couple support structures150 together and/or to other structures. Ignition-risk structure 140 maysupport and/or may be supported by support structure 150. Examples ofignition-risk structures 140 include a fastener, a coupling, astructural joint, a structural edge, a sensor, a wire, a tube, conduit,and/or an enclosure. Ignition-risk structure 140 includes, may becomposed essentially of, and/or may be an electrical conductor.Ignition-risk structure 140 may be electrically conductive (e.g.,metallic) and may be composed essentially of metal. Additionally oralternatively, ignition-risk structure 140 may include, and/or may be, apoor electrical conductor and/or an electrical insulator (electricallynon-conductive).

Ignition-risk structure 140 may be electrically isolated or electricallyconnected to support structure 150. Support structure 150 generally isnon-metallic and may be less electrically conductive than ignition-riskstructure 140. Support structure 150 may include and/or may be anelectrical insulator (electrically non-conductive) and/or a poorelectrical conductor. Support structure 150 may include, and/or may beconstructed of, a polymer (e.g., polyurethane), a composite material(e.g., a carbon fiber-reinforced polymer (CFRP) and/or fiberglass),and/or building materials (e.g., wood, masonry, drywall).

As a specific example of ignition-quenching system 100, theignition-quenching system 100 may be at least a portion of a fuel tank,such as a wing fuel tank in a composite wing aircraft. Ignition-riskstructure 140 may be a fastener exposed to the fuel volume (e.g.,extending into the interior of the fuel tank) and embedded in and/orcoupling one or more support structures 150 which contact the fuelvolume. The support structures 150 may be carbon-fiber composite panels,partitions, stringers, etc. that are in the interior of the fuel tankand/or define at least a portion of the interior of the fuel tank. Theignition-quenching cover 110 covers the ignition-risk structure 140 andis collocated with the ignition-risk structure 140. Theignition-quenching cover 110 is porous and permits fuel vapor to contactthe ignition-risk structure 140. An ignition source associated with theignition-risk structure 140 (fastener) may develop and trigger anignition event at the ignition-risk structure 140. For example, due to,e.g., a lightning strike or the friction of fuel movement, electricalcharge and/or an electrical voltage may develop at the ignition-riskstructure 140 sufficient to cause an electrical discharge or otherpotential ignition source. The ignition event includes an ignitionkernel, a nascent flame front, and/or a pressure wave within theenclosed volume 164 of the ignition-quenching cover 110. The ignitionkernel is quenched by the ignition-quenching cover 110; the nascentflame front is quenched as it traverses the ignition-quenching cover110; and/or the pressure wave may be dissipated and/or impeded by theignition-quenching cover 110.

In addition to mitigating the immediate effects of an ignition event,the ignition-quenching cover 110 may be lighter than a conventional capseal and may permit larger fuel volumes than a conventional cap seal. Inparticular, aircraft wing fuel tanks may include many hundreds offasteners which may be protected by ignition-quenching covers 110. Asmall weight savings in an individual cover may amount to a large netweight savings for the aircraft. Conventional cap seals are not porousand exclude fuel from a volume around each fastener. Ignition-quenchingcover 110 is porous and may permit fuel to substantially fill theenclosed volume 164 and/or the interior volume 166 of theignition-quenching cover 110. The small fuel volume increase associatedwith each ignition-quenching cover 110 may contribute significantly tothe total fuel volume and the efficiency of operation of the aircraft.Further, the resiliency of ignition-quenching covers 110 (generallywithstanding ignition sources and/or ignition events without damage) mayreduce the amount, frequency, and/or complexity of maintenance and/orinspection of the wing fuel tank as compared to a wing fuel tankincorporating conventional cap seals.

Though the aircraft wing fuel tank example is detailed to explain somepotential advantages of use of the ignition-quenching cover 110, theignition-quenching cover 110 may be utilized and/or incorporated withinother examples and/or ignition-quenching systems 100. For example,ignition-quenching cover 110 may be useful in other applicationsrequiring ignition hazard consideration, including fuel transport, fuelstorage, mining operations, chemical processing, metal fabrication,power plant construction and operation, and operations which involvecombustible particulate such as suspended dust, sawdust, coal, metal,flour, and/or grain.

Ignition-quenching cover 110, and components thereof, may be configuredto withstand, and/or to operate at, a wide range of temperatures. Hence,ignition-quenching cover 110 may retain its structural integrity and itsignition-quenching capability when exposed to and/or operating in a hightemperature, a low temperature, and/or temperature cycles. Examples oftemperature extremes and/or ranges include less than 80° C., less than60° C., less than 40° C., less than 20° C., less than 0° C., greaterthan −80° C., greater than −60° C., greater than −40° C., greater than−20° C., and/or greater than 0° C. For example, aircraft may experiencetemperatures in excess of 40° C. (e.g., while on the tarmac) and below60° C. (e.g., while at altitude).

FIG. 4 schematically represents methods 400 of manufacturing,fabricating, forming, and/or assembling an ignition-quenching system(e.g., the ignition-quenching system 100). Methods 400 may be methods ofpreventing bulk combustion of a combustible environment (e.g., thecombustible environment 160) due to an ignition source associated withan ignition-risk structure (e.g., the ignition-risk structure 140).Methods 400 may be methods of protecting a fuel tank from ignitionevents associated with an ignition-risk structure within the fuel tank.

Methods 400 include installing 410 a porous ignition-quenching cover(e.g., the ignition-quenching cover 110) over a portion of theignition-risk structure that is configured to be exposed to thecombustible environment. Installing 410 may include at least partiallyenclosing the portion of the ignition-risk structure with the porousignition-quenching cover. Methods 400 may be methods of installing theignition-quenching cover over a fastener in a fuel tank.

The ignition-risk structure may be coupled to and/or may extend from asupport structure (e.g., the support structure 150). Installing 410 mayinclude affixing and/or coupling the porous ignition-quenching coverdirectly to the ignition-risk structure and/or the support structure.For example, installing 410 may include adhering and/or bonding (e.g.,with adhesive) the porous ignition-quenching cover to the ignition-riskstructure and/or the support structure. Further, installing 410 mayinclude threading, snapping, and/or mechanically interlocking theignition-quenching cover onto the ignition-risk structure and/or thesupport structure. Installing 410 may include coupling the porousignition-quenching cover in direct contact with the ignition-riskstructure and/or the support structure. Installing 410 may includecoupling the porous ignition-quenching cover such that the porousignition-quenching cover is spaced away from at least one of theignition-risk structure and the support structure. Installing 410 mayinclude coupling the porous ignition-quenching cover to form a gapbetween the porous ignition-quenching cover and at least one of theignition-risk structure and the support structure.

Installing 410 the porous ignition-quenching cover may includeintegrally forming, unifying, and/or assembling the ignition-quenchingcover with at least a portion of the ignition-risk structure. Forexample, where the ignition-risk structure includes a bolt and a nut,installing 410 may include unifying the ignition-quenching cover withthe nut and assembling the nut onto the bolt.

Installing 410 the porous ignition-quenching cover may includerepairing, replacing, and/or retrofitting a cover over the ignition-riskstructure. For example, installing 410 may include removing apreexisting cover from the ignition-risk structure, preparing theignition-risk structure to receive and/or to engage the porousignition-quenching cover, and installing the ignition-quenching cover onthe prepared ignition-risk structure.

Methods 400 may include installing 420 the ignition-risk structure ontoand/or into a support structure (e.g., the support structure 150).Installing 420 may include installing the ignition-risk structure in avolume that is configured to at least partially enclose the combustibleenvironment (e.g., within a fuel tank). Further, installing 420 mayinclude exposing at least a portion of the ignition-risk structure(e.g., a portion of the ignition-risk structure that is configured to beexposed to the combustible environment) to the volume.

Methods 400 may include selecting 430 a porous ignition-quenching coversuitable to prevent an ignition event originating at the ignition-riskstructure from propagating through the porous ignition-quenching coverand igniting the bulk of the combustible environment (e.g., selecting,configuring, adapting, and/or fabricating the ignition-quenching cover110).

Methods 400 may include exposing 440 the ignition-risk structure and theporous ignition-quenching cover installed over the ignition-riskstructure to the combustible environment. For example, exposing 440 mayinclude at least partially filling with fuel a fuel tank that includesthe ignition-risk structure and the porous ignition-quenching cover.

FIG. 5 schematically represents methods 500 of manufacturing,fabricating, forming, and/or assembling a porous body (e.g., the porousbody 120) of a porous ignition-quenching cover (e.g., theignition-quenching cover 110).

Methods 500 include selecting 510 a first porous element (e.g., porouselement 130), selecting 520 a second porous element (e.g., porouselement 130), aligning 530 the first porous element and the secondporous element to form an aligned group of porous elements, and joining540 the aligned group of porous elements to form at least a portion ofthe porous body of the ignition-quenching cover. The first porouselement and the second porous element have a respective plurality ofpassages (e.g., passages 126) through the respective porous element. Thefirst plurality of passages and the second plurality of passages have arespective average effective diameter and a respective passageorientation (e.g., passage orientation 132).

Aligning 530 the first porous element and the second porous elementincludes orienting the passage orientation of the first porous elementdifferently than the passage orientation of the second porous element.Aligning 530 may include positioning the first porous element and/or thesecond porous element to form passages (e.g., passages 126) through theporous body. The first porous element and the second porous element mayhave substantially the same characteristics, e.g., one or more ofmaterials, exterior dimensions, exterior shape, size of passages, sizeof pores, orientation of passages (e.g., relative to the exteriorshape), spacing of passages, and/or density of passages.

Additionally or alternatively, the first porous element and the secondporous element may have one or more distinct and/or differentcharacteristics. Aligning 530 may include positioning the first porouselement and/or the second porous element to mis-register and/or misalignthe first plurality of passages and the second plurality of passages,and/or a characteristic of the first porous element and the secondporous element. Aligning 530 may include positioning (e.g., by relativerotation and/or translation) the first porous element and the secondporous element to eliminate any straight-line path through the alignedgroup of porous elements (and/or in the porous body) with an effectivediameter greater than a predetermined threshold such as 1 mm, 0.3 mm,0.1 mm, 0.03 mm, or 0.01 mm.

Joining 540 the aligned group of porous elements may include adhering,bonding, welding, sintering, fastening, and/or coupling the first porouselement and the second porous element together.

Examples of inventive subject matter according to the present disclosureare described in the following enumerated paragraphs.

A1. An ignition-quenching cover configured to quench an ignition eventin a combustible environment triggered by an ignition source associatedwith an ignition-risk structure, the ignition-quenching covercomprising:

a porous body;

wherein the ignition-quenching cover is configured to cover anignition-risk structure, wherein the ignition-risk structure isassociated with a potential ignition source that may produce an ignitionevent in a combustible environment, and

wherein the porous body defines passages sized to quench the ignitionevent.

A2. The ignition-quenching cover of paragraph A1, wherein the porousbody defines a cavity that is configured, sized, and/or shaped toreceive the ignition-risk structure.

A3. The ignition-quenching cover of any of paragraphs A1-A2, wherein theignition source that is at least one of an electrical arc, a hotsurface, a hot particle ejection, and an electrostatic discharge.

A4. The ignition-quenching cover of any of paragraphs A1-A3, wherein theignition source is associated with a buildup of heat and/or electricalcharge in the ignition-risk structure.

A5. The ignition-quenching cover of any of paragraphs A1-A4, wherein theignition-quenching cover is configured to dissipate and/or impede apressure wave associated with the ignition event.

A6. The ignition-quenching cover of any of paragraphs A1-A5, wherein theignition-quenching cover is configured to permit a pressure waveassociated with the ignition event to travel through the porous body.

A7. The ignition-quenching cover of any of paragraphs A1-A6, wherein theignition-risk structure is an electrically conductive structure.

A8. The ignition-quenching cover of any of paragraphs A1-A7, wherein theignition-risk structure is at least one of a fastener, a coupling, ajoint, an edge, a sensor, a wire, a tube, a conduit, and an enclosure.

A9. The ignition-quenching cover of any of paragraphs A1-A8, wherein theignition-risk structure is configured to withstand contact with thecombustible environment.

A10. The ignition-quenching cover of any of paragraphs A1-A9, whereinthe ignition-risk structure is chemically resistant to the combustibleenvironment.

A11. The ignition-quenching cover of any of paragraphs A1-A10, whereinthe ignition-quenching cover is configured to be installed in a fueltank, optionally a wing fuel tank of an aircraft.

A12. The ignition-quenching cover of any of paragraphs A1-A11, whereinthe ignition-quenching cover is configured to withstand a temperature ofless than 80° C., less than 60° C., less than 40° C., less than 20° C.,less than 0° C., greater than −80° C., greater than −60° C., greaterthan −40° C., greater than −20° C., and/or greater than 0° C.

A13. The ignition-quenching cover of any of paragraphs A1-A12, whereinthe ignition-quenching cover is porous to, chemically resistant to,and/or chemically nonreactive with the combustible environment.

A14. The ignition-quenching cover of any of paragraphs A1-A13, whereinthe combustible environment includes one or more of a fuel and anoxidizer, and optionally wherein the fuel includes at least one ofhydrogen, gaseous hydrocarbon, aerosolized hydrocarbon, liquidhydrocarbon, and suspended particulate.

A15. The ignition-quenching cover of any of paragraphs A1-A14, whereinthe combustible environment includes at least one of a gas, an aerosol,and a vapor.

A16. The ignition-quenching cover of any of paragraphs A1-A15, whereinthe porous body is a multicomponent and/or multilayer porous body thatincludes at least two porous elements, and optionally wherein a passageorientation of at least one of the at least two porous elements isdifferent than a passage orientation of at least another of the at leasttwo porous elements.

A17. The ignition-quenching cover of any of paragraphs A1-A16, whereinthe porous body includes, and optionally is, one or more (optionally twoor more) porous elements, and optionally wherein each porous element isindependently selected from the group consisting of a reticulatedlattice, a reticulated foam, and an open-cell foam.

A18. The ignition-quenching cover of any of paragraphs A1-A17, whereinthe porous body and/or any included porous elements has a mass densityof at most 2 g/cc, at most 1 g/cc, at most 0.5 g/cc, at most 0.2 g/cc,at most 0.1 g/cc, at most 0.05 g/cc, at most 0.02 g/cc, or at most 0.01g/cc.

A19. The ignition-quenching cover of any of paragraphs A1-A18, whereinthe porous body and/or at least one, optionally each, included porouselement has a porosity of at least 50%, at least 75%, at least 85%, atleast 90%, at least 95%, or at least 98%.

A20. The ignition-quenching cover of any of paragraphs A1-A19, whereinthe porous body and/or at least one, optionally each, included porouselement has an average effective pore diameter and/or an averageeffective passage diameter that is less than or equal to a quenchingdistance of the combustible environment.

A21. The ignition-quenching cover of any of paragraphs A1-A20, whereinthe porous body and/or at least one, optionally each, included porouselement has an average effective pore diameter and/or average effectivepassage diameter that is at least 0.1 mm, at least 0.2 mm, at least 0.5mm, at least 1 mm, at least 2 mm, at least 3 mm, at most 10 mm, at most3 mm, at most 1 mm, at most 0.3 mm, and/or at most 0.1 mm.

A22. The ignition-quenching cover of any of paragraphs A1-A21, whereinthe porous body and/or at least one, optionally each, included porouselement includes struts that define a reticulated lattice, optionallywherein one or more, and optionally all, of the struts are hollow strutsand/or hollow tubes.

A22.1. The ignition-quenching cover of paragraph A22, wherein the strutshave a diameter that is at most 75%, at most 50%, at most 25%, at most10%, and/or at most 5% of an average effective pore diameter and/or anaverage effective passage diameter.

A22.2. The ignition-quenching cover of any of paragraphs A22-A22.1,wherein the hollow struts and/or the hollow tubes contain aflame-suppressing substance, optionally a haloalkane.

A23. The ignition-quenching cover of any of paragraphs A1-A22.2, whereinthe porous body and/or at least one, optionally each, included porouselement includes, and/or is composed essentially of, one or more ofpolypropylene, polystyrene, polyurethane, ethylene vinyl acetate,polysulfone, a composite material, a carbon fiber-reinforced polymer,fiberglass, a ceramic, a glass, a non-metal, a metal, aluminum, steel,and titanium.

A24. The ignition-quenching cover of any of paragraphs A1-A23, whereinthe porous body and/or at least one, optionally each, included porouselement is electrically conductive or electrically insulating.

A25. The ignition-quenching cover of any of paragraphs A1-A24, whereinthe porous body and/or at least one, optionally each, included porouselement has a volumetric specific heat capacity that is at least 10times, at least 100 times, or at least 1,000 times a volumetric specificheat capacity of the combustible environment.

A26. The ignition-quenching cover of any of paragraphs A1-A25, whereinthe porous body and/or at least one, optionally each, included porouselement has a total heat capacity that is at least 3 times, at least 10times, or at least 30 times a total heat capacity of the combustibleenvironment within a volume defined by the porous body.

A27. The ignition-quenching cover of any of paragraphs A1-A26, whereinthe porous body and/or at least one, optionally each, included porouselement has a thermal conductivity that is at least 5 times, at least 10times, at least 100 times, or at least 1,000 times a thermalconductivity of the combustible environment.

A28. The ignition-quenching cover of any of paragraphs A1-A27, whereinthe porous body and/or at least one, optionally each, included porouselement is configured to prevent a hot particle of greater than apredetermined size associated with an ignition source from passingthrough the porous body.

A29. The ignition-quenching cover of any of paragraphs A1-A28, whereinthe porous body has a shape that is configured to avoid a coronadischarge at an exterior surface of the ignition-quenching cover.

B1. An ignition-quenching system for preventing bulk combustion in acombustible environment by an ignition source associated with anignition-risk structure, the ignition-quenching system comprising:

a support structure that is in contact with a combustible environment;

an ignition-risk structure that extends and/or protrudes from thesupport structure into the combustible environment; and

a porous ignition-quenching cover that substantially covers theignition-risk structure and that is coupled to the support structure,wherein the porous ignition-quenching cover is configured to quench anignition event in the combustible environment triggered by an ignitionsource associated with the ignition-risk structure.

B2. The ignition-quenching system of paragraph B1, wherein the porousignition-quenching cover is the ignition-quenching cover of any ofparagraphs A1-A29.

B3. The ignition-quenching system of any of paragraphs B1-B2, whereinthe porous ignition-quenching cover is collocated with the ignition-riskstructure.

B4. The ignition-quenching system of any of paragraphs B1-B3, whereinthe porous ignition-quenching cover substantially encloses at least aportion of the ignition-risk structure that is in contact with thecombustible environment.

B5. The ignition-quenching system of any of paragraphs B1-B4, whereinthe ignition-risk structure is coupled to the support structure.

B6. The ignition-quenching system of any of paragraphs B1-B5, whereinthe porous ignition-quenching cover is directly coupled to the supportstructure.

B7. The ignition-quenching system of any of paragraphs B1-B6, whereinthe porous ignition-quenching cover is affixed to the support structure,optionally with an adhesive.

B8. The ignition-quenching system of any of paragraphs B1-B7, whereinthe porous ignition-quenching cover is spaced apart from the supportstructure, optionally by a distance that is less than a quenchingdistance of the combustible environment.

B9. The ignition-quenching system of any of paragraphs B1-B8, whereinthe porous ignition-quenching cover is coupled to the ignition-riskstructure.

B10. The ignition-quenching system of any of paragraphs B1-B9, whereinthe porous ignition-quenching cover is threaded onto, snapped onto,and/or mechanically interlocked with the ignition-risk structure.

B11. The ignition-quenching system of any of paragraphs B1-B10, whereinthe porous ignition-quenching cover is affixed to the ignition-riskstructure, optionally with an adhesive.

B12. The ignition-quenching system of any of paragraphs B1-B11, whereinthe porous ignition-quenching cover is integrally formed with at least aportion of the ignition-risk structure.

B13. The ignition-quenching system of any of paragraphs B1-B12, whereinthe porous ignition-quenching cover is spaced apart from theignition-risk structure.

C1. A method of preventing bulk combustion of a combustible environmentby an ignition source associated with an ignition-risk structure, themethod comprising:

installing a porous ignition-quenching cover over an ignition-riskstructure, wherein the installing the porous ignition-quenching coverincludes at least partially enclosing the ignition-risk structure;

wherein the porous ignition-quenching cover is configured to quench anignition event triggered by an ignition source associated with theignition-risk structure.

C2. The method of paragraph C1, wherein the porous ignition-quenchingcover is the ignition-quenching cover of any of paragraphs A1-A29, andoptionally wherein the method comprises selecting the ignition-quenchingcover.

C3. The method of any of paragraphs C1-C2, further comprising installingthe ignition-risk structure in a volume that is configured to at leastpartially enclose the combustible environment, and optionally whereinthe installing the ignition-risk structure includes exposing theignition-risk structure to the volume.

C4. The method of any of paragraphs C1-C3, wherein the installing theporous ignition-quenching cover includes at least one of affixing andcoupling the porous ignition-quenching cover, optionally directly, tothe ignition-risk structure.

C4.1. The method of paragraph C4, wherein the installing the porousignition-quenching cover includes adhering the porous ignition-quenchingcover to the ignition-risk structure, optionally with an adhesive.

C5. The method of any of paragraphs C1-C4.1, wherein the installing theporous ignition-quenching cover includes at least one of affixing andcoupling the porous ignition-quenching cover, optionally directly, to asupport structure from which the ignition-risk structure extends and/orprotrudes.

C5.1. The method of paragraph C5, wherein the installing the porousignition-quenching cover includes adhering the porous ignition-quenchingcover to the support structure, optionally with an adhesive.

C6. The method of any of paragraphs C1-05.1, wherein the installing theporous ignition-quenching cover includes installing the porousignition-quenching cover in a fuel tank, optionally an aircraft fueltank.

C7. The method of any of paragraphs C1-C6, wherein the installing theporous ignition-quenching cover includes retrofitting the ignition-riskstructure to include the ignition-quenching cover by removing apreexisting cover from the ignition-risk structure, preparing theignition-risk structure to receive the porous ignition-quenching cover,and installing the ignition-quenching cover on the ignition-riskstructure.

C8. The method of any of paragraphs C1-C7, further comprising exposingthe ignition-risk structure and the porous ignition-quenching coverinstalled over the ignition-risk structure to the combustibleenvironment.

C9. The method of any of paragraphs C1-C8, wherein the combustibleenvironment is the combustible environment of any of paragraphs A1-A29.

C10. The method of any of paragraphs C1-C9, wherein the installing theporous ignition-quenching cover includes installing the porousignition-quenching cover over a portion of the ignition-risk structurethat is configured to be exposed to a combustible environment.

D1. A method of assembling a porous body of an ignition-quenching cover,the method comprising:

selecting a first porous element with a first plurality of passagesthrough the first porous element, wherein the first plurality ofpassages has a first average effective diameter and a first passageorientation;

selecting a second porous element with a second plurality of passagesthrough the second porous element, wherein the second plurality ofpassages has a second average effective diameter and a second passageorientation;

aligning the first porous element and the second porous element to forman aligned group of porous elements, wherein the aligning includesorienting the first passage orientation differently than the secondpassage orientation; and

joining the aligned group of porous elements to form a porous body of anignition-quenching cover.

D2. The method of paragraph D1, wherein the porous body is the porousbody of any of paragraphs A1-A29.

D3. The method of any of paragraphs D1-D2, wherein theignition-quenching cover is the ignition-quenching cover of any ofparagraphs A1-A29.

D4. The method of any of paragraphs D1-D3, wherein the first averageeffective diameter and the second average effective diameter areapproximately equal.

D5. The method of any of paragraphs D1-D4, wherein the aligning includespositioning the first porous element and the second porous element toeliminate any straight-line path through the aligned group of porouselements with an effective diameter greater than a predeterminedthreshold such as 1 mm, 0.3 mm, 0.1 mm, 0.03 mm, or 0.01 mm.

As used herein, the terms “adapted” and “configured” mean that theelement, component, or other subject matter is designed and/or intendedto perform a given function. Thus, the use of the terms “adapted” and“configured” should not be construed to mean that a given element,component, or other subject matter is simply “capable of” performing agiven function but that the element, component, and/or other subjectmatter is specifically selected, created, implemented, utilized,programmed, and/or designed for the purpose of performing the function.It is also within the scope of the present disclosure that elements,components, and/or other recited subject matter that is recited as beingadapted to perform a particular function may additionally oralternatively be described as being configured to perform that function,and vice versa. Similarly, subject matter that is recited as beingconfigured to perform a particular function may additionally oralternatively be described as being operative to perform that function.Further, as used herein, the singular forms “a,” “an,” and “the” may beintended to include the plural forms as well, unless the context clearlyindicates otherwise.

The various disclosed elements of systems and apparatuses, and steps ofmethods disclosed herein are not required of all systems, apparatuses,and methods according to the present disclosure, and the presentdisclosure includes all novel and non-obvious combinations andsubcombinations of the various elements and steps disclosed herein.Moreover, any of the various elements and steps, or any combination ofthe various elements and/or steps, disclosed herein may defineindependent inventive subject matter that is separate and apart from thewhole of a disclosed system, apparatus, or method. Accordingly, suchinventive subject matter is not required to be associated with thespecific systems, apparatuses and methods that are expressly disclosedherein, and such inventive subject matter may find utility in systemsand/or methods that are not expressly disclosed herein.

As used herein, the phrase, “for example,” the phrase, “as an example,”and/or simply the term “example,” when used with reference to one ormore components, features, details, structures, embodiments, and/ormethods according to the present disclosure, are intended to convey thatthe described component, feature, detail, structure, embodiment, and/ormethod is an illustrative, non-exclusive example of components,features, details, structures, embodiments, and/or methods according tothe present disclosure. Thus, the described component, feature, detail,structure, embodiment, and/or method is not intended to be limiting,required, or exclusive/exhaustive; and other components, features,details, structures, embodiments, and/or methods, including structurallyand/or functionally similar and/or equivalent components, features,details, structures, embodiments, and/or methods, are also within thescope of the present disclosure.

As used herein, the phrases “at least one of” and “one or more of,” inreference to a list of more than one entity, means any one or more ofthe entities in the list of entities, and is not limited to at least oneof each and every entity specifically listed within the list ofentities. For example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently, “at least one of A and/or B”)may refer to A alone, B alone, or the combination of A and B.

The invention claimed is:
 1. An ignition-quenching cover configured toquench an ignition event in jet fuel vapor triggered by an electricalarc, a hot particle ejection, or an electrostatic discharge associatedwith an electrically conductive fastener extending into an interior of afuel tank, the ignition-quenching cover comprising: a porous body thatincludes two or more porous elements; wherein the porous body has aproximal cover side and a distal cover side opposite the proximal coverside, wherein the proximal cover side defines a recess that is sized andshaped to receive and engage the electrically conductive fastenerextending into the interior of the fuel tank to cover the electricallyconductive fastener extending into the interior of the fuel tank, andwherein the porous body defines passages sized to quench the ignitionevent.
 2. The ignition-quenching cover of claim 1, wherein a passageorientation of at least one of the two or more porous elements isdifferent than a passage orientation of at least another of the two ormore porous elements.
 3. The ignition-quenching cover of claim 1,wherein each porous element is independently selected from the groupconsisting of a reticulated lattice, a reticulated foam, and anopen-cell foam.
 4. The ignition-quenching cover of claim 1, wherein theporous body has a mass density of at most 0.5 grams per cubic centimeter(g/cc).
 5. The ignition-quenching cover of claim 1, wherein the porousbody has an average effective passage diameter that is less than aquenching distance of the jet fuel vapor.
 6. The ignition-quenchingcover of claim 1, wherein the porous body is configured to prevent a hotparticle of greater than a predetermined size from passing through theporous body along a straight line trajectory.
 7. The ignition-quenchingcover of claim 1, wherein the ignition-quenching cover is configured todissipate or impede a pressure wave associated with the ignition event.8. The ignition-quenching cover of claim 1, wherein theignition-quenching cover is configured to permit a pressure waveassociated with the ignition event to travel through the porous body. 9.The ignition-quenching cover of claim 1, wherein the ignition-quenchingcover is chemically nonreactive with the jet fuel vapor.
 10. Theignition-quenching cover of claim 1, wherein the porous body has aporosity of at least 50%.
 11. The ignition-quenching cover of claim 1,wherein the porous body has an average effective pore diameter that isat most 0.3 mm.
 12. The ignition-quenching cover of claim 1, wherein theporous body includes struts that define a reticulated lattice.
 13. Theignition-quenching cover of claim 12, wherein the struts have a diameterthat is at most 75% of an average effective passage diameter of thepassages of the porous body.
 14. The ignition-quenching cover of claim12, wherein the struts are hollow and contain a haloalkane.
 15. Theignition-quenching cover of claim 1, wherein the porous body has a shapethat is configured to avoid a corona discharge at an exterior surface ofthe ignition-quenching cover.
 16. The ignition-quenching cover of claim1, wherein the recess is configured to thread onto, snap onto, and/ormechanically interlock with the electrically conductive fastenerextending into the interior of the fuel tank.
 17. The ignition-quenchingcover of claim 16, wherein the porous body comprises threads, snap-fitstructure, and/or mechanical interlock structure that at least partiallydefines the recess.
 18. A method comprising: installing theignition-quenching cover of claim 1 over the electrically conductivefastener extending into the interior of the fuel tank, wherein theinstalling the ignition-quenching cover includes at least partiallyenclosing the electrically conductive fastener within the recess of theignition-quenching cover, wherein the fuel tank is a composite structurefuel tank.
 19. The method of claim 18, further comprising exposing theelectrically conductive fastener and the ignition-quenching coverinstalled over the electrically conductive fastener to the jet fuelvapor.
 20. The method of claim 18, wherein the installing theignition-quenching cover includes coupling the ignition-quenching coverto at least one of the electrically conductive fastener and thecomposite structure fuel tank.
 21. The method of claim 18, furthercomprising installing the electrically conductive fastener in a fuelvolume of the composite structure fuel tank.